We buy bulk eggplant at our local farmer's market (you can stuff a fairly large bag full for $5). Go home and peel, slice, parboil (for 2 to 3 minutes), dunk in ice water, then place on towels to drain. Once drained, we put on a large cookie tray to freeze before sealing with our seal-a-meal (the eggplant is too watery to seal properly otherwise).
We pull out bags of the eggplant during winter and spring to add to pasta sauce or make baba ganoush.
I haven't frozen squash before, but if it's like eggplant, the unfrozen consistency will be somewhat mushy. Our eggplant, for example, isn't capable of frying after it's been frozen. You can freeze the squash the same way (slice and parboil, cool off, etc.), but it will be best used in casserole/sauce type dishes.
I've also made squash casseroles and frozen them (squash layered with onions/sausage/cheese sauce), and the frozen version is slightly mushier than making the casserole fresh...but still very good.
An aunt of mine would freeze large stuffed zucchini. She'd parboil the whole zucchini for a few minutes until it was semi-soft, cool it off, cut in half, scoop out the inside and make boats. Then she'd use the scooped out part and mix with cooked rice or bread pieces, sauted onions and garlic, spices, cooked meat (shrimp or crumbly sausage or hamburger), and a little cheese with an egg binder. She'd put the stuffing in the zucchini boat, wrap really well with saran wrap, and freeze. Defrost overnight and heat in the oven inside of the stuffing was thoroughly cooked.
She'd also make eggplant parm and freeze. I've never tried her stuffed zucchini or parm recipes on my own, but they were delicious when she'd defrost and heat them for dinner.